1. Field of the Invention
This invention relates to regulator circuits, and more particularly to regulator circuits for providing a plurality of currents having regulated magnitudes with desired temperature characteristics and which are suitable for being fabricated in monolithic integrated circuit form.
2. Discussion of the Prior Art
Present day electronic circuits and systems often require current supplies or sources which provide currents having regulated magnitudes that are independent of supply voltage but have a particular temperature coefficient. More particularly, it is sometimes desirable to utilize a current supply circuit providing a current with a magnitude that has a positive temperature coefficient and which varies directly with absolute temperature. The current can be exploited to cancel the negative temperature coefficient inherent in the PN junctions of a differential pair of transistors, for instance, so as to enable the provision of a composite differential amplifier that has a gain which remains substantially constant with temperature change. Since a single integrated circuit can include several such differential pairs, it can require a plurality of currents all having magnitudes with positive temperature coefficients which vary directly with absolute temperature. To solve this problem it is sometimes desirable to provide current references capable of operating a plurality of controlled current supplies, each of which provides a current to a different portion of an integrated circuit, for instance.
Prior art circuits or cells have been developed which are useful in generating reference signals having positive temperature coefficients. U.S. Pat. No. 3,908,162, "Voltage and Temperature Compensating Source" of Robert R. Marley et al, which is assigned to the same assignee as the subject application, and U.S. Pat. No. 3,930,172 of Robert C. Dobkin, each disclose circuits or cells for providing reference signals having desired temperature coefficients to some kinds of electrical loads. The reference cells disclosed by the aforementioned patents, if formed of NPN transistors are not suitable for individually and simultaneously driving a plurality of NPN current control transistors in some applications. NPN current supply transistors are usually preferred to PNP types in monolithic integrated circuits because monolithic NPN transistors have Betas which are much greater than the Betas of monolithic PNP transistors. Specifically, these prior art circuits rely on a plurality of NPN transistors having base-to-emitter junctions connected serially in a loop with each other and a resistor, such that the summation of the base-to-emitter voltages develop a desired output reference voltage across the resistor. Furthermore, the magnitudes of the collector currents of these transistors, which have their collector-to-emitter paths connected in series, must be equal. If these circuits are called upon to drive a plurality of NPN current supply transistors then large currents are drawn from the loop and the collector currents become unequal. Consequently the prior art reference circuits tend to function improperly when required to drive one of the most desirable types of loads.